The small intestine transports large quantities of fluid daily and this fluid exits the intestinal interstitium by either the lymphatic and/or the vascular systems. Any changes in capillary forces that favor filtration will result in a decrease in intestinal movement of solvent across the mucosa. We propose to measure simultaneously from an in situ ileal loop of the cat the direction and magnitude of changes in the Starling Forces under a variety of physiological and pharmacological challenges imposed on the intestine. The forces to be measured are capillary hydrostatic pressure, interstitial fluid pressure, lymph and plasma colloid osmotic pressure, lymph and blood flows and intestinal fluid volume. In addition, we will investigate the relationship between blood flow and oxygen extraction in the overall delivery of oxygen to meet the metabolic needs of the intestine during physiological/pharmacological challenges.